function region()
    local x = {}
    local vx = {}
    local mass = {}
    local rho = {}
    local p = {}
    local u = {}
    local itype = {}

    local ntotal = 4
    local nvirt = 0
    x[1] = {}
    x[2] = {}
    vx[1] = {}
    vx[2] = {}
    x[1][1] = 0.0
    x[2][1] = 0.0
    x[1][2] = 0.0
    x[2][2] = 1.0
    x[1][3] = 1.0
    x[2][3] = 1.0
    x[1][4] = 1.0
    x[2][4] = 0.0

    for i = 1, 4 do
        vx[1][i] = 0.0
        vx[2][i] = 0.0
        p[i] = 1000.0 * 9.8 * (1.0 - x[2][i])
        rho[i] = p[i] / (c * c) + 1000.0
        mass[i] = 1.0 * 1.0 * rho[i]
        u[i] = 357.1
        itype[i] = 10 -- 淡水
    end

    return x, vx, mass, rho, p, u, itype, 1.0, ntotal, nvirt
end
